1. Field of the Invention
This invention relates to oil-in-water emulsions for use as defoamers in pulp and paper mill applications. The defoamer comprises an oil blend (of a triglyceride oil or a mixture of triglyceride oils and silicone), a stabilizing agent (to make the oil blend stable in the emulsion), hydrophobic silica particles, surfactants, dispersants, and other components. The emulsion is usable directly at low concentrations to control foam
2. Description of Related Art
Defoamers are needed in pulp and paper mills to 1) reduce unwanted foam and thereby enhance water drainage from the pulp mat, 2) minimize loss of process chemicals, and 3) increase equipment capacity. Continued improvement of defoamer technology is highly desirable, particularly with respect to cost effectiveness, compliance with environmental regulations, and reduction of unwanted contaminants in pulp and paper products.
Among defoaming applications, pulp and paper mill applications involving black liquors are considered the most challenging. Kraft black liquor is found at different concentrations and compositions in different Kraft mills and can even be different at different stages within the same mill. For illustration, a Kraft black liquor may contain 33% lignin, 27% organic acids, 23% inorganic components, 6% extractives (such as wood resins, fatty and resin acids, di- and triglycerides, steryl esters, sterols, etc.), and 11% bound sodium. Many of these components (such as fatty acids, lignin, and wood resin fractions) are natural foam stabilizers. Note that the fatty and resin acids are in saponified/salt forms at the alkaline pH of the black liquor. In addition, chemical additives also add to the surfactant load, especially in the paper mill. Particulates, such as paper fines and fillers can also stabilize foam under some conditions. Furthermore, the black liquor in the mill entails high temperatures and high pH.
Additional pulp and paper applications of defoamers include their use in sulfite pulping process and in effluent and other water treatment. For many of these applications, the use of triglyceride oils may be particularly attractive because they are perceived to be less toxic and more “green” than other oils. Deformers used in pulp and paper applications may also be used for other non-food industrial uses.
Whereas many defoamers are known, the most effective pulp mill defoamers are oil-in-water emulsions based on silicone. In an oil-in-water emulsion, water constitutes the continuous phase. A simplified silicone defoamer for pulp mill applications consists of four components: 1) water, 2) silicone, 3) hydrophobic silica particles, and 4) one or more dispersants, surfactants, and additives. Within this general scheme, there are a variety of different defoamer formulations possible, differing in the composition or functionality, number of components, nature of the materials chosen, and the process of manufacturing.
Defoamer emulsions are difficult to manufacture, requiring specific compositions and processes to produce stable emulsions. If the emulsion “breaks” and phase separation occurs, the defoamer decreases in efficacy, in addition to the problem of fouling and deposit formation. Thus, a successful defoamer emulsion has to satisfy the requirement of foam minimization and emulsion stability. It must also be microbiologically inert. In addition, if the defoamer emulsion can improve drainage, it has an enhanced value.